1. Field of the Invention
The present invention relates to a temperature measuring device and a level measuring device using the temperature measuring device.
2. Description of the Related Arts
In a continuous casting process, for example, accurate measurement of temperature and surface level of molten steel during casting is necessary for improving the product quality and the production yield. A conventional technique for measuring the temperature of molten steel in a tundish and a mold involves preparing a solidification chamber inside of a carbon sleeve to introduce the molten steel, and determining the temperature in the solidification chamber using a contact thermometer of a consumable immersion thermocouple type or a thermocouple covered with a ceramic protective tube. As for the method to determine the level of molten steel, conventional art uses an eddy-current distance detector.
The above-described consumable immersion thermocouple degrades after only one measurement because it directly contacts the molten steel. Therefore, the probe to measure the temperature is detachable at the tip of the thermometer, and the tip probe is replaced in every measurement. Since such probes are expensive and are discarded in every measurement, an increase of the number of measurements is difficult.
In the case that the thermocouple is covered with a ceramic tube, the thermocouple does not contact directly with the molten steel. Consequently, a continuous measurement is possible. In this case, however, the durability of ceramic protective tube has a limitation because of heat shock and erosion caused by slag. As a result, even if an expensive protective tube is used, it is generally durable only to 40 to 50 hrs., and repeated use for a long time is impossible.
Still further, with respect to the eddy-current distance detector which is used to determine the level of molten steel, it is useful to achieve level control in accordance with a precise measurement under a steady state condition. The conventional range of measurement, however, is as narrow as 200 mm or less, so such detectors can not be used to determine the level during an automatic start-up. Consequently, automatization to achieve an automatic start-up mode is difficult.